1. Field of the Invention
The present invention relates to a thermoelectric element having excellent thermoelectric characteristics, which is favorably used for cooling the heat-generating members such as semiconductors.
2. Description of the Related Art
A thermoelectric element utilizing the Peltier effect is simple in construction, easy to handle, stably maintains its characteristics and is, hence, drawing attention concerning a use over a wide range of applications. In particular, owing it its locally cooling performance and precise temperature control near room temperature, the thermoelectric element has been utilized as a thermoelectric module being electrically connected and arranged on a support substrate in a device (semiconductor laser, optical integrated circuit, etc.) which must be precisely controlled to remain at a constant temperature and in small refrigerators.
If the thermoelectric element utilizing the Peltier effect is placed under the poorly heat-radiating conditions, the temperature of the whole element is raised due to the Joule heat generated in the element, and it becomes no longer possible to maintain the temperature of the element constant. To avoid such an inconvenience, it has been attempted to set the shape of the thermoelectric element used for the thermoelectric module to lie within a predetermined range. This is to control the amount of heat radiation needed by the element during the operation at a maximum efficiency to effect efficient cooling by defining optimum dimensional values of the thermoelectric element. For example, Japanese Unexamined Patent Publication (Kokai) No. 125963/1998 (prior art A) teaches realizing a stable and high energy conversion efficiency by setting a shape factor (L/S) expressed by a ratio of the element thickness L to the element sectional area S to lie within a range of from 300/m to 1200/m.
In each thermoelectric module, there are usually arranged several tens of thermoelectric elements (p-type thermoelectric element) comprising the p-type semiconductors and several tens of thermoelectric element (n-type thermoelectric element) comprising the n-type semiconductors. Japanese Unexamined Patent Publication (Kokai) No. 97472/1996 (prior art B) teaches increasing the number of the thermoelectric elements is effective, i.e., increasing the number of the elements (element density) per a unit area, is effective in increasing the cooling efficiency of the thermoelectric module.
According to the thermoelectric element taught in the prior art A, however, the shape factor L/S is as small as from 300/m to 1200/m, the sectional area of the element is large, the element density in the thermoelectric module is as small as about several tens per a square centimeter, and heat is not absorbed in sufficiently large amounts.
The thermoelectric module has a structure as schematically illustrated in FIG. 1, wherein n-type thermoelectric elements 2 and p-type thermoelectric elements 3 are alternately arranged on a support substrate 1 and are electrically connected in series through wiring conductors 4, the thermoelectric elements 2 and 3 being in a rectangular parallelepiped shape having a width W and a length (thickness) L. According to the prior art B, the thermoelectric element has a bottom surface of a square shape of a width W (sectional area S of the element is expressed by W2), and the sectional area S of the element is decreased to increase the element sequences on the support substrate by one sequence in both the vertical direction and the lateral direction, in order to increase the element density. According to the prior art B, therefore, the shape of the thermoelectric element inevitably becomes slender since the sectional area S of the element is small. As the shape of the thermoelectric element becomes slender, however, breakage and deformation of the elements easily occur while the module is being assembled. This tendency becomes conspicuous as the shape factor (L/S) increases. There further occurs such a problem that the module that has been assembled loses the mechanical strength and the shock resistance, and exhibit deteriorated characteristics.
According to the conventional thermoelectric element as described above, it is difficult to set the shape factor to be an optimum value or to increase the element density for being used in the thermoelectric module, and the cooling efficiency is not obtained as desired.